Abstract:

The study area included low-grade metamorphic units representing the Karakaya Complex (Lower Karakaya-LKC) outcropping in the Armutlu-Ovacık zone in the Armutlu Peninsula. In this study, samples were collected during field work in the Iznik and Yenişehir (Bursa) regions, and petrographic (optical microscope, SEM) and mineralogical (XRD) examinations were performed. Among the LKC units, the Iznik Metamorphics are represented by greenstone facies rocks (metasandstone, slate, schist, quartzite, metagabbro, metavolcanic, dolomitic marble). Quartz, phyllosilicate (illite, chlorite, C-V, kaolinite, I-V, smectite, stilpnomelane, paragonite, antigorite), feldspar, calcite, pyroxene (augite), dolomite, amphibole (hornblende, tremolite/actinolite, anthophyllite) and opaque minerals (hematite and goethite) were identified in descending order of abundance among the LKC unit. The trioctahedral chlorites with chamosite composition had the IIb polytype, whereas the illites had 2M1 and 2M+1M polytypes. The Kübler Index (KI; Δ2) values were in the range of 0.19-0.41 Δ2 (mean: 0.25 Δ2), which indicates epi-metamorphic and very low metamorphic grade. The AI (Δ2) values were in the range of 0.26-0.32 Δ2 (mean: 0.29 Δ2), which is compatible with the Kübler Index data from illites. Dioctahedral illites with phengite compositions had b0 values (Å) in the range of 8.952-9.030 Å (mean: 8.995 Å), and they were in the low- to moderate-pressure facies sequence. Comparing the lithological, mineralogical and crystal chemistry parameter data (crystallinity, polytype and b0) of the Iznik metamorphics representing LKC to those of equivalent units found in central-northeastern Anatolia (Nilüfer Unit and Turhal Metamorphics), the unit showed diagenesis-metamorphism conditions with greenstone facies corresponding to the upper part of the Lower Karakaya (LKC-UP). Petrographic and mineralogical data (paragenesis, KI, AI, b0, index mineral associations) revealed that the Iznik Metamorphics were affected by lower greenschist (high anchizone-epizone) metamorphism during the Permian-Early Cretaceous period.

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